Certain specialized aircraft are designed to fly long distances and stay aloft for long periods of time. These are sometimes known by the acronym “HALE”—high altitude long endurance. However, the aircraft need not necessarily fly at high altitudes. These aircraft are typically unmanned, remotely controlled and are useful or potentially useful in a variety of applications. For example, in surveillance to conduct aerial patrols along a border, or along a coast of a nation or state, or in remote areas to act as a substitute for a “cell tower” for cellular communications. For such uses, it is desirable that these aircraft have the capability to remain aloft for long periods (more than about three days) and traverse a significant area during that time. Accordingly, the aircraft carry a relatively large quantity of fuel to enable long endurance, whether deployed at high or low altitude.
Typically, these aircraft present a large external surface area: they tend to have very large wings relative to fuselage length, typically more than about 3.0. Because fuel is typically stored in the wings, the design of these large wings is generally a compromise between the requirements of “lift” to launch and maintaining the aircraft aloft, and the requirement for fuel storage. In these types of craft there is an additional trade off between reduction in weight (and hence fuel requirements) to extend mission capability versus the increased weight necessary to carry sufficient fuel for long endurance. One approach to meeting these conflicting requirements might be to use solar power but technology to demonstrate flight longer than about 24 hours has not yet been developed. The use of lighter than air stratospheric airships has been proposed but while these achieve high altitude and can stay aloft for days, they are expensive and susceptible to cross winds and so lack the path stability required to carry out missions that require a fixed path of flight.
Accordingly, it is desirable to develop an aircraft that could be deployed at high or low altitude that has long endurance and directional stability under most of the expected conditions encountered when aloft. In addition, it would be a benefit if the wings could be designed optimally for flight conditions rather than as a compromise with necessary fuel carrying capability in the wings. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.